- Branche: Earth science
- Number of terms: 93452
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Founded in 1941, the American Congress on Surveying and Mapping (ACSM) is an international association representing the interests of professionals in surveying, mapping and communicating spatial data relating to the Earth's surface. Today, ACSM's members include more than 7,000 surveyors, ...
The quantity hQ calculated using the function ( ∫ g(H) dH) / τ <sub>fφ</sub>, in which g(H) is the measured value of gravity acceleration at elevation H, τ <sub>fφ</sub> is the acceleration τ <sub>o</sub> calculated from a standard gravity formula for the latitude φ and corrected by half the free air gravity correction δg <sub>f</sub>. Integration is from point P <sub>o</sub> on the geoid to the point P <sub>n</sub> vertically above it on the surface. (τ <sub>fφ</sub> ≡ τ <sub>φ</sub> + δg <sub>f</sub>/2). Physically, it is intended to be the distance, taken along the vertical, between the geoid at latitude φ and the geop through the point P <sub>n</sub> whose elevation is wanted (free air gravity is calculated at the mid point between the two surfaces). It is therefore the same as dynamic height except that free air gravity is used instead of standard gravity.
Industry:Earth science
A monumented survey station at which is placed equipment used in obtaining locations of an aircraft taking photographs.
Industry:Earth science
An apparatus for determining gravity acceleration by dropping an object so that it falls vertically in a vacuum and measuring the amount of time it takes for the body to fall through a known distance. If the distance the body falls is determined by shining a vertical beam of coherent radiation onto the object and counting changes in the number of wavelengths from the source to the object, the apparatus may be called a laser gravimeter or laser-type gravity apparatus.
Industry:Earth science
A device composed of one or more flat mirrors mounted and arranged so that a beam of sunlight reflected by the mirrors can be aimed in any desired direction. The heliostat was invented by Gauss. Placed at one survey station, a heliostat is used to direct a beam of sunlight toward another, distant survey station where the light can be observed through a theodolite. It provides an excellent target to which horizontal directions can be measured; such targets have been observed at distances approaching 300 kilometers. There are several types of heliostat, known by various names. However, these devices differ only in details of mechanical arrangement and construction.
Industry:Earth science
The finest line normally produced in printing, approximately 0.08 to 0.1 mm thick.
Industry:Earth science
A grid used in polar regions and based on the Greenwich meridian.
Industry:Earth science
The bearing, on a map having a grid, from a north south line of the grid to a line drawn on the grid.
Industry:Earth science
A plane parallel to an average position of the Earth's axis of rotation and at an angle to the plane of the Greenwich Meridian by an amount defined by the Bureau International de l'Heure (B.I.H.) in such a way that time reckoned from this plane agrees with the Universal Time 2 determined by the B.I.H. The plane is close to that of the Greenwich Meridian.
Industry:Earth science
The stereoscopic model formed by viewing the overlap of two adjacent right-hand or left-hand exposures of convergent photographs.
Industry:Earth science
Any quantity derived from a gravity anomaly by subtracting one or more gravity corrections from it.
Industry:Earth science
